Informed by geographic information system (GIS) methodologies, this epidemiologic investigation will quantify secular changes in socioeconomic gradients in breast cancer incidence in the United States, among both women and men. To date, no studies have directly addressed this question. Our 3-prong hypothesis is that: (a) the social class gradient is decreasing over time, because (b) incidence rates are rising more quickly among persons residing in less affluent areas, and (c) similar patterns are evident among women and men, reflecting the impact of nonreproductive risk factors, both environmental and anthropometric. To test our hypothesis, we will obtain cancer data from the Northern California Cancer Center (NCCC), covering 5 counties in the San Francisco Bay Area (1973-2002; n approximately 70,000 females cases; 490 male cases), the Los Angeles Cancer Surveillance Program (1973- 2002; n approximately 129,400 female cases; n - 940 male cases); and the Massachusetts Cancer Registry (1982-2002; n approximately 93,100 female cases; 760 male cases), along with relevant 1970 to 2000 US census data. We will then use GIS methodologies to append to each cancer registry record, based on each patient's residential address, geocodes for latitude, longitude, census block group, and census tract, generate state-of-the-art census block group and tract area-based socioeconomic measures, and link each geocoded record to the relevant area-based socioeconomic measures. We next will generate relevant denominators stratified by the area-based socioeconomic measures, using data from the 1970-2000 decennial censuses for periods straddling each census, and explore methods to estimate intercensal population counts. As a first step in testing our hypothesis, we will calculate and compare age standardized average annual breast cancer incidence rates stratified by the area-based socioeconomic measures for each registry for calendar periods 1979-1981, 1989-1991, and 1999-200 l. Building on these preliminary analyses, we will then employ geoadditive models, including time trend models and smoothing methodologies, to test the hypothesis that the socioeconomic gradient in breast cancer incidence is declining over time (1973-2002) among both women and men, and examine the sensitivity of these analyses to different denominator estimates. Results of this investigation will provide new insights into social determinants of and secular changes in breast cancer incidence, with implications for breast cancer surveillance, screening and control.